Improvement in assay sensitivity for plasma dolastatin-10 using capillary electrophoresis at elevated temperatures

The very potent antimitotic and anticancer agent, dolastatin-10 (DOL-10), currently undergoing testing in a phase II clinical trial, has been quantitated previously in human plasma by high-performance capillary electrophoresis (HPCE). This method provides a lower limit of detection of 25 ng/ml DOL-10 from extracted patient samples. Without changes in preconcentration techniques, we report a significant improvement in the sensitivity of this method using elevated temperatures with conventional UV absorbance detection and liquid-liquid extraction which lowers the detection limit to 3 ng/ml of the drug. An elevated separation temperature of 50 degrees C was critical in achieving this 8x improvement in the detection limit. Partial validation of the method at this temperature gave excellent linearity (0-100 ng/ml; y=0.018x+0.085, r=0.993), limit of quantitation (5 ng/ml), and good overall recovery of the drug (>85%). We have applied this improved method towards the in vivo quantitation of DOL-10 in mice and in a patient receiving the drug in a phase I clinical study. From these analyses we conclude that this method is suitable for clinical studies where plasma levels of DOL-10 are > or = 5 ng/ml.